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UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 869 

Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 



Washington, D. C. 



PROFESSIONAL PAPER 



September 30, 1920 



THE INHERITANCE OF THE LENGTH 

OF INTERNODE IN THE RACHIS 

OF THE BARLEY SPIKE 



By 

H. K. HAYES, Head of Section of Plant Breeding, Division of 
Agronomy and Farm Management, College of Agriculture, Uni- 
versity of Minnesota, and HARRY V. HARLAN, Agronomist in 
Charge of Barley Investigations, Office of Cereal Investigations 



CONTENTS 



Page 

Scope of the Experiments 1 

Historical Review 1 

Pure-Line Varieties Used in These 

Studies 3 

Reliability of Experimental Methods . . 4 
Effects of Environment and Varying 

Sources of Seed on Density .... 5 



Purity of Parental Forms ...... 5 

Inheritance of Length of Internodes in 

Crosses between Pure Lines .... 9 

Summary of Results 20 

Discussion of Results 21 

Conclusions 24 

Literature Cited 25 




WASHINGTON 
GOVERNMENT PRINTING OFFICE 

1920 



OCT 



•f 3* 

21 mm 






UNITED STATES DEPARTMENT OF AGRICULTURE 




I BULLETIN No. 869 

uffl mf „ .... ........ -s 



jru^"^«-ft. 



Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 




jrLr?"«£7L 



Washington, D. C. 



PROFESSIONAL PAPER 



September 30, 1920 



THE INHERITANCE OF THE LENGTH OF INTER- 
NODE IN THE RACHIS OF THE BARLEY SPIKE. 

By H. K. Hayes, Head of Section of Plant Breeding, Division of Agronomy and Farm 
Management, College of Agriculture, University of Minnesota, and Harry V. Har- 
lan, Agronomist in Charge of Barley Investigations, Office of Cereal Investigations. 



CONTENTS. 



Scope of the experiments 

Historical review 

Pure-line varieties used in these studies 

Reliability of experimental methods 

Effects of environment and varying sources 

of seed on density 

Purity of parental forms 



Page. ] Page. 

1 | Inheritance of length of internodes in crosses 

1 between pure lines 9 

3 Summary of results 20 

4 Discussion of results 21 

Conclusions 24 

Literature cited 25 



SCOPE OF THE EXPERIMENTS. 

In 1915 a series of studies on the inheritance of the length of 
internode in the rachis of the barley spike was begun in cooperation 
with the Minnesota Agricultural Experiment Station. Internode 
length is a particularly favorable character for such investigations, 
as a large number of varieties furnish many gradations in internode 
length and in a pure line the average internode length of the rachis 
varies comparatively little from year to year. 

The project was undertaken for two main reasons, (1) as a study 
of inheritance in an unusually favorable size character and (2) as a 
contribution to the question of the taxonomic value of the length of 
internode of the rachis. 

HISTORICAL REVIEW. 

The length of internode is frequently referred to as density, and 
both terms are used in this bulletin. As far back as Linnaeus, species 
were differentiated by this character. With fertility, it has been, 
consciously or unconsciously, one of the main bases of classification 

182694°— 20— Bull. 869 1 



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2 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 

of most of the modern taxonomists as well. The groups of Schuebler 
(22) 1 , Seringe (23), Heuze" (11, 12), Voss (25), Koernicke (13, 14, 15, 
16, 17), Atterberg (2, 3, 4), and Beaven (5) involved variations in 
density. In 1918 Harlan (10) offered an arrangement which elim- 
inated the question of density from the major groups. It was re- 
tained as a minor distinction only, because of the volume of the liter- 
ature in which it had been used. Its complete elimination would 
have left too little connection between the author's scheme and the 
previous usage. 

In classifying barleys, density is an obvious and attractive char- 
acter. When confined to type forms the separations are ideal, but, 
as with many things in taxonomy, its perfection depends on limited 
material. The more material that is assembled the more the sub- 
divisions of density have to be increased. Linna?us (18) used the 
name Hordeum distichon to designate the lax 2-rowed and H. zeo- 
criton to designate the very dense 2-rowed forms. Schuebler divided 
H. disticlion into erectum and nutans. Eriksson (S) used genuinum 
and patens to designate lax and dense subdivisions of erectum. 
Linnaeus recognized Jiexasticlium and vulgar e as the dense and lax 
groups of 6-rowed barleys. Koernicke divided hexasticlium into 
pyramidatum and paraUelwm and recognized hrachyurum and macro- 
terium of Alefeld (1) as dense and lax subdivisions of pyramidatum. 
The finer the groups were made, the more confusing became the dis- 
tinctions. The confusion indicated that, while there might be some 
genetic distinctions, from a taxonomic standpoint there was no clear 
separation. 

In the mode of inheritance the situation is also complicated. As 
a size character, the accounts are quite favorable as to its constancy, 
and some varieties are traceable for centuries by this character alone. 
In recent times Blaringhem (7), possibly following the lead of the 
Svalof station, made quite elaborate studies of barley density in 
France. Harlan (9) found density to be quite a stable character. 
Regarding the mode of inheritance, the studies, however, are largely 
unsatisfactory. The taxonomic papers contain no comprehensive 
measurement of density. Many of the inheritance papers are equally 
inadequate. In many instances fertility and density are treated 
together, as by Von Tschermak (24). Density has been regarded 
as recessive by Blaringhem (7) and as dominant by Von Tschermak. 

The only paper which is directly concerned with the method of 
study used in this article is that of Biffen (6), who obtained results 
closely parallel to those presented herein. In three crosses to which he 
paid particular attention, Biffen found the F 1 generation to be slightly 
more dense than the lax parent, although the numbers of individuals 
in Fj were small. The F 2 generation consisted in each case of plants 

1 The serial numbers in parentheses refer to "Literature cited," at the end of this bulletin. 



INHERITANCE IN THE BARLEY SPIKE. 3 

with spikes as lax or as dense as those of the parents, with a series 
lying between these extremes which could not be satisfactorily classi- 
fied without further test. In some crosses the F 2 generation curves 
plotted from the measurements showed two peaks and in others three. 
In a cross of zeocriton X nutans groups of plants were centered about 
internode lengths of 2.2 and 3 millimeters, respectively. The 65 
plants constituting the more dense group were tested in the F 3 
generation by seeding all individuals with internode lengths ranging 
from 1.8 to 2.6 millimeters. Of these 65 plants, 55 proved homozy- 
gous and 10 were heterozygous. Thus, 55 out of a total of 209 plants 
grown in F 2 bred true for densities near that of the dense parent, or 
a close approximation of a 1 : 3 ratio. No genetic analysis is given of 
crosses which appear to have three groups in F 2 , or lax, dense, and 
intermediate forms. 

Study has been made of the inheritance of density in wheat and, 
although apparently pertinent, it is not comparable to one made in 
barley, for the reason that the dense wheats are clubbed at the tip 
and thus introduce a condition which makes comparison difficult. 
Gradations were found in F 2 between the parents. Nilsson-Ehle (20) 
explained these on the basis of two kinds of factors, a positive factor 
for compactness which partially inhibited the action of one or more 
lengthening factors. Parker (21), in a more extensive study in which 
the statistical method was used, concludes that numbers such as 
Nilsson-Ehle used were inadequate to demonstrate his hypothesis. 
In Parker's studies segregation occurred in F 2 , but it seemed impos- 
sible to determine the number of factors involved. 

PURE-LINE VARIETIES USED IN THESE STUDIES. 

With the exception of the Jet variety, the pure lines used in crosses 
in the studies here reported are quite typical representatives of the 
three degrees of density much used by taxonomists in the 6-rowed 
barley. Their relationships are most easily made apparent by use of 
the taxonomic key which follows. The variations in density are well 
shown in Plate I. 

KEY TO BARLEY VARIETIES USED IN DENSITY STUDIES. 

Hordeum vulgare pallidum (6-rowed, hulled, awned, white). 

Subvariety typica, spike lax, pure-line Manchuria. 

Sub variety parallelum, spike dense, pure-line Reid Triumph. 

Subvariety pyramidatum, spike very dense, pure-line Pyramidatum. 
Hordeum distichon palmella (2-rowed, hulled, awned). 

Subvariety nutans, spike lax, pure lines Hanna and Steigum. 

Subvariety erectum, spike dense, pure-line Svanhals. 

Subvariety zeocriton, spike very dense, pure-line Zeocriton. 

Jet is a naked, black, 2-rowed barley of about the same spike 
density as Steigum. Although Hanna and Steigum belong to the 
same group, Steigum is slightly more dense than Hanna. Dejiciens 



4 BULLETIN 869, TJ. S. DEPARTMENT OF AGRICULTURE. 

was not used in any of the crosses, but is included because of an 
inherited variation found in it. The form used is lax and differs 
from nutans in having only rudiments of lateral florets. 

RELIABILITY OF EXPERIMENTAL METHODS. 

In this investigation the feasibility and accuracy of density deter- 
minations were tested in many ways. The length of internode was 
computed from the measurement of 10 internodes in the middle, of 
the spike. All measurements were taken in millimeters. 

To test the observational accuracy, the populations from wnich the 
density of three parents was determined were remeasured after a lapse 
of three weeks. The difference in the measurements of Manchuria 
was 0.02 ±0.01 mm.; of Zeocriton, 0.04 ±0.01 mm.; and of Hanna, 
0.12 ±0.02 mm." Differences as small as 0.2 mm. in means of varie- 
ties, therefore, can not be demonstrated by the method used. As 
seasonal fluctuations in the means often are as great as this, the 
method of taking the data is sufficiently accurate. 

The internode measurement was taken in the middle of the spike, 
not only because of the greater convenience, but because experiments 
indicated that the internodes in this zone are less variable than in 
other parts of the spike. Measurements were taken in different parts 
of the spike on approximately 100 plants of each of the Zeocriton, 
Pyramidatum, Manchuria, and Hanna parents. Where the spikes 
were long enough, six different sections were measured, i. e., nodes 
1-11, 3-13, 5-15, 7-17, 11-21, and the last 10 internodes toward the 
tip. In Pyramidatum the measurements for nodes 7-18 and 11-22 
could not be made. The means for these measurements, in milli- 
meters, were as follows: Zeocriton, 1.37, 1.47, 1.66, 1.81, 1.95, and 
2.15; Pyramidatum, 1.98, 2.12, 2.17, and 2.15; Manchuria, 2.88, 
3.13, 3.35, 3.42, 3.36, and 3.38; Hanna, 3.90, 4.17, 4.40, 4.47, 4.35, 
and 3.90. 

The Zeocriton is the only variety in which there is a progressive 
increase in internode length from the base to the tip. If the factor 
or factors determining this progressive increase segregate in a normal 
way, the progeny of a cross between this type and one in which this 
peculiarity is absent or less pronounced, as in Pyramidatum, might 
contain types easily misinterpreted. The mean of a pure recessive 
for a main density factor might easily differ by 0.2 to 0.4 mm. from 
the parent, due to the gain or loss of this marked progressive increase 
of internode length found in Zeocriton. 

Contrary to results previously reported by Harlan (9), no change 
in internode length due to the presence of sterile nodes was observed. 



Bui. 869, U. S. Dept. of Agriculture. 



Plate I. 




Bui. 869, U. S. Dept. of Agriculture. 



PLATE I I . 




INHERITANCE IN THE BARLEY SPIKE. 

EFFECTS OF ENVIRONMENT AND VARYING SOURCES OF SEED ON 

DENSITY. 

Wide differences of condition, such as obtain in California as com- 
pared with Minnesota, are. sufficient to modify the expression of 
density. As will be seen by referring to Table I, the annual fluctua- 
tions of density measurements in a pure variety are not sufficient in 
Minnesota to introduce any large error in the conclusions, especially 
when it is considered that progeny are compared only with parents 
of the same year's growth. 

In 1918 there was an opportunity to test the effect of vigor of plant 
on density. One section of the nursery produced Manchuria plants 
which averaged 110 centimeters in height, while the same strain in 
another part of the nursery averaged only 82 centimeters. A similar 
difference was apparent in Svanhals. The internode lengths of the 
Manchuria plants were 3.36 ±0.01 and 3.33 ±0.01 mm., respectively, 
and of Svanhals, 2.56 ±0.01 and 2.65 ±0.01 mm., respectively, both 
being within the limits of observational accuracy. 

Sometimes the F x generation of a cross was grown in the Washing- 
ton greenhouse and the seed from it was still rather immature when 
sown in Minnesota. Plants of Manchuria from greenhouse seed gave 
a mean internode length of 3.22 ±0.02 mm., as compared with 
3.34 ±0.02 mm. in plants from field-grown seed. In Svanhals, the 
difference was less, 2.49 ±0.02 as compared with 2.52 ±0.01 mm. 
Neither variation is large enough to have any particular significance 
in this study. 

PURITY OF PARENTAL FORMS. 

The variation which may be expected in a pure line within a single 
season and from season to season is shown in Table I. The 6-rowed 
varieties gave about the same mean average length of internode in 
all three seasons. With the 2-rowed varieties there was more seasonal 
fluctuation in average density. All varieties of this group gave a 
higher mean length of internode in 1918 than in 1917. In Steigum 
the seasonal difference reached its maximum of 0.51 ±0.03 mm., 
and in Hanna the seasonal variation also was large. Individuals 
of different densities in the different varieties were selected as 
parents. The only possibility of inherited variation within the same 
variety occurred in dejiciens. The progeny of plant 333-5-1 is sig- 
nificantly lower in mean density. Only two or three, deficiens types 
have been grown in the nursery, and the progeny showed no evidence 
of hybridization. As the chance of mixture or accidental crossing 
is small, it might be interpreted that we had chanced to select a spike 
in which a sudden change in the factors for density had taken place. 



BULLETIN 860, U. S. DEPARTMENT OF AGRICULTURE. 






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INHERITANCE IN THE BARLEY SPIKE. 9 

INHERITANCE OF LENGTH OF INTERNODES IN CROSSES BETWEEN 

PURE LINES. 

Each cross studied has been considered as a separate family. 
For convenience, the data from each such family will be discussed 
separately. In considering crosses, statements will be made as to 
the number of homozygous and heterozygous forms. Such state- 
ments can be only relative. Using the variability of the pure lines 
as a standard, it is assumed that progeny lines of low variability are 
homozygous, while those ot high variability are heterozygous. There 
is no reasonable doubt of the classification of the extremes, but there 
is a borderland where the most varying homozygotes may be in doubt. 

FAMILY MANCHURIA (360) X SVANHALS (458). 

The actual F x generation of the cross between Manchuria and 
Svanhals, which was the basis of later generations discussed in this 
bulletin, was grown in 1915. A considerable number of crosses 
between these same pure lines of Manchuria and Svanhals were made 
in 1917 in the greenhouse at Washington, D. 0. The data for the F t 
reported in Table II (sec. A) are from this greenhouse seed. On the 
basis of the coefficient of variability, this F t generation proved 
no more variable than the parents. 

In 1917 the mean average density in millimeters of the Svanhals 
parent was 2.53 ±0.01 mm.; of the Manchuria, 3.34 ±0.01 mm.; and 
of the F ly 2.70 ±0.01 mm. There is almost a complete dominance of 
the dense over the lax form. 

An F 2 generation was grown both in 1916 and in 1918. The means 
for these two F 2 generations were 2.94 ±0.01 and 2.96 ±0.02 mm., 
respectively. The variation as determined by the frequency distri- 
bution and the coefficient of variability was much greater in F 2 than 
in F x or in the parental forms, the coefficient of variability of the Fj 
generation being 6.30 ±0.30 mm. and of the F 2 generations of 1916 
and 1918, 10.20 ±0.27 and 11.82 ±0.48 mm., respectively. 

Thirty-two F 3 lines, representing all F 2 types of density, were 
grown. Thirteen of these F 2 plants appeared to give homozygous 
progeny in the F 3 generation. The writers recognize that too few 
plants were grown in F 3 to determine with certainty which forms 
were homozygous. Eight of these 13 lines were continued in F 4 , and 
five of these appeared to be homozygous. These results show that a 
considerable number of the F 2 plants selected bred true in F 3 , although 
no conclusion as to the actual percentage can be made. 

The five types which proved to be homozygous in F 4 gave mean 
densities as follows: 378-1, mean 2.57 ±0.01 mm.; 378-11, mean 
2.64 ±0.01 mm.; 378-14, mean 3.37 ±0.02 mm.; 378-23, mean 2.55 ± 
0.01 mm.; 378-31, mean 2.58 ±0.01 mm. Selection 378-88 gave the 
highest coefficient of any third-generation line. Two heads were 
selected which bred true in F 4 for densities near the Manchuria parent. 
182694°— 20— Bull. 869 2 



10 



BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 



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.INHERITANCE IN THE BARLEY SPIKE. 15 

The Svanhals parent gave a mean of 2.71 ±0.01 mm. and the 
Manchuria one of 3.46 ±0.01 mm. in 1918. No sorts were obtained 
which were homozygous for densities very different from those of 
the parents. 

FAMILY MANCHURIA (360) X STEIGUM (17). 

The parental forms of the Manchuria and Steigum cross gave 
nearly the same average density in 1916. In 1918 the Manchuria 
parent gave about the same average density as in 1916, but the 
Steigum averaged somewhat higher than in the previous year. The 
coefficient of variability of the Manchuria parent in 1917 was 4.19 ± 
0.15 mm.; of the Steigum parent, 4.90±0.17 mm.; and of the F 2 gen- 
eration which was grown in 1916, 7.69 ±0.21 mm. The data are 
reported in Table II (sec. B). 

As Table II shows, some forms bred true in F 3 and in F 4 , while 
others were as variable as the F 2 generation. Selection 368-22 in 
the F 3 and F 4 generations gave means of 3.21 ±0.02 and 3.29 ±0.01 
mm., respectively. When compared with the parental forms, it 
seems that we have here a lower density line than either parent. As 
the number of individuals is small in many F 3 lines, it does not seem 
profitable to analyze more closely the results obtained. 

FAMILY PYRAMIDATUM (476) X JET (454). 

Table II (sec. C) shows that the parental forms of the cross between 
Pyramidatum and Jet are of very different densities. The Pyrami- 
datum parent gave a mean density of 2.11 ±0.01 mm. in 1918; 
the Jet, 3.92±0.01 mm.; while the F x generation averaged 2.86±0.01 
mm. The F t generation is, therefore, slightly more dense than the 
parental average, which is 3.01 mm. This is quite different from the 
F x generation in the cross between Manchuria and Svanhals, in which 
there was an almost complete dominance offline dense over the 
lax form. / 

The F 2 generations were grown both m^J&lG and in 1918. The 
means for these two F 2 generations were about the same as the 
parental average, being 2.92 ±0.04 mm. and 3.10 ±0.03 mm., respec- 
tively. The highest coefficient of variability for the Jet parent is 
6.93 ±0.39 mm., while the highest coefficient for Pyramidatum is 
6.16 ± 0.21 mm. The coefficients of variability for the two F 2 genera- 
tions are 16.44 ±0.87 mm. and 18.38 ±0.81 mm., respectively, while 
the frequencies of the F 2 generations range from above the modal 
class of the lax parent to the modal class of the dense parent. It is 
of interest to note that with a total of 87 Fi plants, none were of the 
same frequency range as that of the parents, all being of intermediate 
density. Of the 22 F 2 plants continued in F 3 , ten would have been 
included within the limits of this F x population. Of these ten, eight 
gave about as variable a progeny as the F 2 generation, while two 



16 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 

appeared to give homozygous dense progeny. Of the entire 22 
plants, representing all types of F 2 densities, nine proved about as 
variable in F 3 as the F 2 generation. 

Seven F 3 selections which appeared to be breeding true, as deter- 
mined by the frequency distribution and coefficient of variability, 
were tested in the F 4 generation. This was done by selecting 10 heads 
of different densities and growing the progeny of each separately. 
Where all heads gave similar results, they are combined in the table 
and are given as the result of 10 plants. 

The F 3 line 325-5, of which only 26 plants were available for study, 
gave a mean of 3.15 ±0.02 mm. in 1917, with a low coefficient of 
variability. On testing this line in 1918, when data from 213 plants 
were available, a somewhat higher mean was obtained, or 3.43 ±0.01 
mm. Its coefficient of variability is also somewhat larger than in 
the homozygous parental forms. Selection 325-15 proved pure in 
F 4 with the exception of the progeny of one plant which gave as 
great a variability as the F 2 generation. Why one plant should 
behave so differently from the nine others is difficult to explain. 
The possibility of a natural cross must not be overlooked, although 
observations show that these are very infrequent. An occasional 
error is also a possibility, although precautions, were taken to elimin- 
ate these as far as possible. 

The F 4 means for the seven lines which gave evidence in F 3 and F 4 
indicating that they were homozygous are as follows: 325-5 (10 
plants), 3.43 ±0.01 mm.; 325-13 (10 plants), 3.47 ±0.01 mm.; 
325-16 (9 plants), 3.74 ±0.01 mm.; 325-18 (10 plants), 2.24 ±0.01 
mm.; 325-20 (10 plants), 2.47 ±0.02 mm.; 325-21 (10 plants), 
3.95 ±0.01 mm.; 325-22 (10 plants), 3.72 ±0.01 mm. 

Of these, five have mean densities which are not very different 
from that of the Jet (lax) parent, while the means of the other two 
are similar to that of the Pyramidatum parent. The most dense 
and the least dense of the five lax homozygous segregates have mean 
internode lengths of 3.43 ± 0.01 mm. and 3.95 ± 0.01 mm., respectively. 
As great a difference as this in any one season would not be expected 
in a sort homozygous for similar characters. It is not much greater, 
however, than seasonal variation in the means of several of the pure 
2-rowed forms, which seem more susceptible to such variability 
than the 6-rowed parents. Inheritance of such a reaction difference 
might possibly explain the results here represented. Whatever expla- 
nation may be given for these new means, here, as in the Man- 
churia X Svanhals cross, no homozygous forms were produced 
which differed materially in density from the density of one or the 
other parent. 



INHERITANCE IN THE BARLEY SPIKE. 17 

FAMILY HANNA (460) X REID TRIUMPH (404). 

The parental forms, Hanna and Reid Triumph, are of distinctly 
different densities, and there is no overlapping of frequency distri- 
butions during the three years in which they have been grown. In 
Table II (sec. D) the mean of the Hanna parent ranges from 
4.12±0.02 mm. in 1916 to 4.56±0.01 mm. in 1918. The Reid 
Triumph variety has much less seasonal variation, the mean in 1917 
being 2.73 ±0.01 mm. and in 1916, 2.64 ±0.01 mm. It is of interest 
to note that the Reid Triumph has about the same average mean as 
the Svanhals 2-rowed form, while the Hanna is considerably more 
lax than the Manchuria form which was crossed with the Svanhals 
variety. 

The F 2 generation of the cross between Hanna and Reid Triumph 
proved more variable than the parents and frequently gave distri- 
bution from below the mode of the Reid Triumph to considerably 
above the mode of the Hanna parent. Twenty F 2 plants were grown 
in F 3 , some giving as variable a population as obtained in F 2 , while 
other F 3 lines were no more variable than the parental forms. 

Fourteen of these F 3 lines which gave the clearest indication of 
being homozygous were further tested in the F 4 generation. The 
method was similar to that previously used, 4 to 10 plants of a line 
being grown and the combined result being the basis of conclusions 
as to purity. Of the 14 lines tested in F 4 , 8 gave evidence in the com- 
bined F 3 and F 4 data to show that they are homozygous for density. 

Those which are of questionable purity will be briefly considered. 
Selection 406-3 gave a mean of about the same density as the Reid 
Triumph parent, but the coefficient of variability is somewhat higher 
than in the pure parental lines. Selection 406-4 proved to be 
heterozygous. One of the head selections, 406-4-3, produced a type 
which seems pure for density. The mean of this line is 3.72 ±0.03 
mm. Selection 406-9 seems to be heterozygous. Probably 406-9-1 
is homozygous, the average mean being about the same as that of 
the Hanna parent. Selection 406-10 also is more variable than the 
pure parental variety. The frequency distribution indicates that 
fewer density factors are involved than in the F 2 generation. Selec- 
tions 406-16 and 406-18 appear to be heterozygous. In later gen- 
erations two selections of 406-18 seem to be homozygous. Thus 
406-18-5 is probably breeding true with a mean density of 3.40 ±0.02 
mm,, while 406-18-9 gives evidence of being homozygous for a 
mean of 2.66 ±0.02 mm. 

Those which seem nearly homozygous by an examination of their 
frequency ranges and coefficients of variability as obtained in F 3 
and F 4 generations are as follows: 406-1, mean 2.81 ±0.01 mm.; 
406-5, mean 4.43 ±0.01 mm.; 106-7, mean 2.43 ±0.01 mm.; 406-8, 
mean 4.32 ±0.01 mm.; 406-11, mean 4.32±0.02 mm.; 406-12, mean, 



18 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 

2.84 ±0.02 mm.; 406-19, mean 3.29 ±0.01 mm.; 406-22, mean 
4.37 ±0.01 mm. 

Aside from these, individual heads grown in F 4 which appear to 
give homozygous progeny as a result of the single season's test are 
as follows: 406-4-3, mean 3.72±0.03 mm.; 406-9-1, mean 4.30±0.04 
mm.; 406-18-5, mean 3.40 ±0.02 mm.; 406-18-9, mean 2.66 ±0.02 
mm. 

The means for these' four F 4 families are somewhat unreliable 
because of the small number of individuals grown. All coefficients 
of variability, however, are very small. 

These results show that homozygous intermediates may be pro- 
duced, as well as homozygous types, which give about the same aver- 
age density as the parental forms. No analysis of average differ- 
ences as small as 0.2 to 0.3 mm. has been attempted. The fact that 
environmental or other seasonal characters may modify the expres- 
sion of a character nullifies such close analysis. 

FAMILY HANNA (460) X ZEOCRITON (1039). 

The Hanna used in the cross with Zeocriton is the same pure line 
that was used in the cross with Reid Triumph. Zeocriton is a very 
dense 2-rowed form. This cross is between the most dense and the 
most lax form used in this study. 

The F 3 generation shown in Table II (sec. E) ranged from above 
the modal class of Hanna to the modal class of Zeocriton, even though 
only 141 individuals were studied. It has a correspondingly high 
coefficient of variability. 

An examination of the coefficients obtained in later generations 
show that some are as large as those obtained in the F 2 line. Others 
are intermediate, being significantly larger than any obtained in the 
pure forms, while still others are as small as those obtained for the 
pure parental lines. This would indicate that the mode of inheritance 
was more complex than in the cross between Pyramidatum X Jet 
previously mentioned. 

Selection 448-9, which was almost as variable in the F 3 as in the 
F 2 generation, was selected for further experiment, the progeny of 
30 plants being measured in the F 4 generation. Data from 7 of the 
30 progeny lines are presented, as the remaining 23 all appeared to 
be segregating. Results of density studies in F 4 lines 448-9-7, 
448-9-14, 448-9-16, and 448-9-29 are given, as these indicate the 
segregation obtained in the unpresented lines. No F 4 line of greater 
coefficient of variability than 448-9-7 was obtained, and none with a 
wider frequency range than 448-9-16. Three lines appear to be 
homozygous, as determined by the frequency distribution and coeffi- 
cient of variabilitv. These are shown in Table III. 



INHERITANCE IN THE BARLEY SPIKE. 



19 



Table III. — Homozygous plants of selection 448-9 of the Hanna-Zeocriton cross, F 4 

generation. 



Fi line. 



448-9-4. 
448-9-19 
448-9-30 



Number of 
individuals. 



Mean. 



Millimeters. 
2.06±0.01 
3.41± .04 
4.30± .02 



Coefficient of 
variability. 



6.80±0.41 
7.33± .87 
4.65± .29 



The mean of 448-9-19 is not as reliable as of the other two lines, 
as only 16 individuals were available for the study. 

Selections 448-7 and 448-13 appear heterozygous in the F 3 genera- 
tion and have about the same degree of frequency range. The coeffi- 
cients of variability are much smaller than in F 2 , but are significantly 
larger than in the pure parental forms. The frequency range for 
448-7, of which 39 plants were studied, was from 2.0 to 3.2 mm. 
Two plants from each of these lines gave evidence of being homozy- 
gous in F 4 . These are shown in Table IV. 

Table IV. — Homozygous plants of selections 448-7 and 448-13 of the Hanna-Zeocriton 

cross, F t generation. 



F t line. 


Number of 
individuals. 


Mean. 


Coefficient of 
variability. 


448-7-1 


107 
102 
64 
57 


Millimeters. 
2. 21 ±0.01 
3.12± .01 
3.19± .02 
4.15± .02 


7.69±0.35 


448-7-3 


5.77± .27 


448-13-2 


6.27± .37 


448-13-5 


4.58± .29 







Four of the 20 F 2 plants which were tested in F ? appeared to give 
homozygous progeny. Three of these proved to be homozygous by 
further test, while one, 448-11, proved heterozygous. The F 4 lines of 
interest which seem to be homozygous are shown in Table V. 

Table V. — Homozygous plants of selection 448-11 of the Hanna-Zeocriton cross, F 4 

generation. 



F t line. 


Number of 
individuals. 


Mean. 


Coefficient of 
variability. 


448-11-2 


73 
45 


Millimeters. 
3.08±0.01 
3.69± .02 


5.52±0.31 


448-11-3 


4.34± .31 







The three lines of especial interest which appeared homozygous by 
both the F 3 and F 4 study are as follows: 448-1, mean 2.30 ± .01 mm. ; 
448-5, mean 2. 88 ±.01 mm.; 448-16, mean 4. 30 ±.01 mm. The F 4 
generation means are given for these lines, as they are based upon 
larger numbers than the F 3 test. Typical spikes of the parent 
varieties and of these lines are shown in Plate II. 



20 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 

In the Hanna X Zeocriton cross there are a number of homozygotes 
of a density intermediate between the densities of the parents. The 
homozygotes of this cross appear to fall in groups. Three near the 
dense parent have internode lengths ranging from 2.06 to 2.30 mm. 
Three near the lax parent have internode lengths ranging from 4.15 
to 4.30 mm. Four moderately dense intermediates have internode 
lengths varying from 2.88 to 3.19 mm., and two lax intermediates 
have internode lengths of 3.41 and 3.69 mm. This grouping is arbi- 
trary, as the difference between the two intermediate groups is little 
more than between individuals of either intermediate group. Some 
homozygous intermediates from this cross have densities approxi- 
mately the same as those of parents used in other crosses studied. 

SUMMARY OF RESULTS. 

- The observational accuracy is such that differences in density 
greater than 0.2 mm. are significant when the measurements are 
taken in the middle part of the spike. 

Except in the Hanna and Steigum varieties the seasonal fluctua- 
tions in the means of the parents were not more than 0.2 mm. The 
seasonal variations in the means of the 2-rowed were greater than in 
the 6-rowed varieties. 

The density of the ¥ l generation does not have an unvarjmig relation 
to the density of the parents. In the Svanhals X Manchuria cross 
density is dominant in the F x generation. In the Pyramidatum X Jet 
cross it was intermediate. 

The two F t generations grown were no more variable than the 
parental sorts and all crosses gave segregation hi F 2 . Although the 
number of F 2 plants grown averaged no greater than that of the 
parental forms, the frequency ranges extended from the modal class 
of one parent to the modal class of the other and often beyond these 
classes. 

The F 3 generation contained progeny groups which were no more 
variable for length of rachis internode than pure lines of the parents. 
Rather extensive studies of a number of F 4 generations gave further 
evidence of purity of several of these F 3 lines. 

The Manchuria X Svanhals and Pyramidum X Jet crosses gave 
forms homozygous for densities similar to those of the parents but 
none homozygous for intermediate densities. Crosses between Hanna 
and Reid Triumph and between Hanna and Zeocriton gave types 
homozygous for densities intermediate between the densities of the 
parents, as well as near those of their parents. The latter cross pro- 
duced homozygous forms similar to Reid Triumph, Hanna, and their 
homozygous intermediates, as well as forms like the Zeocriton parent. 
The range of means of these homozygous forms was almost continu- 
ous, although there was an indication of two centers of intermediate 



INHERITANCE IN THE BARLEY SPIKE. 21 

density. More extensive study would be needed to determine whether 
these apparent centers are of any significance. 

DISCUSSION OF RESULTS. 

From the fact that segregates homozygous for density are apparent 
in the measurements of the F 3 and F 4 generations, it seems safe to 
conclude that internode length in the barley rachis may be explained 
on the factor hypothesis. The number or value of the factors involved 
is not readily estimated. In a general way the results of the Man- 
churia X Svanhals and the Pyramidatum x Jet crosses seem to 
indicate a single main factor difference. The proportion of homo- 
zygotes is roughly satisfactory, and the absence of homozygotes differ- 
ing greatly from the mean of their parents is also in favor of this 
belief. The dominance of density in the F x generation in the first 
cross and its intermediate expression in the second is of interest. 

The results in the Hanna X Reid Triumph cross in the same way 
indicate a broad difference of two factors. In this cross forms were 
isolated that were homozygous for intermediate densities, as well as 
forms having densities near those of the parents. These results can 
be interpreted very satisfactorily on the basis of two main factors 
for internode length. These factors are cumulative in effect, both 
being necessary to produce the extreme type. The results show that 
a sort may be homozygous for one of the factors and heterozygous 
for the other. At least, heterozygous forms whose progeny range is 
from the intermediate group to one or the other parent are so 
interpreted. 

The Hanna X Zeocriton cross gave homozygous intermediates of 
unlike value, as well as homozygous sorts which were like the parents. 
If the presence and absence hypothesis is here used, three main 
factors may be postulated to explain the genetic facts. These factors 
may be supposed to be of like value, each inherited independently, 
each allelomorphic to its absence, the number showing a hetero- 
zygous condition being half the homozygous sorts. This hypothesis 
explains the genetic fact fairly well. Other minor factor differences 
are doubtless necessary to explain all of the results. One known 
minor character of some density significance separates the parental 
forms. This is a difference in the progressive density from the base 
to the tip of the rachis, the Zeocriton parent being the only sort 
which shows a constant increase in length of internode from the base 
to the tip of the spike. 

A comparison of the Pyramidatum x Jet cross with the Hanna X 
Zeocriton cross illustrates some facts regarding the mode of inherit- 
ance of density. These are the two widest crosses made in the study. 
The first produced no homozygous intermediates. The second pro- 
duced many. An F x generation was grown of the Pyramidatum X 



22 



BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 



Jet cross. It was of intermediate density and no more variable than 
the parental forms. The second generation is shown in figure 1 as 
a multimodal curve with peaks at densities corresponding to those of 
the parents and the F x generation. The homozygous forms pro- 
duced closely approximated the densities of the parental varieties, as 
is illustrated by the curves. Although there is considerable varia- 
bility in the means of the more lax segregates, this is no greater than 
the seasonal variation of the means of several of the 2-rowed forms. 

The contrast between the Pyramidatum x Jet and the HannaX 
Zeocriton crosses is very striking. Each showed wide segregation 



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30 



20 



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1 

1 
1 
1 


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1 


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Fig. 1.— Diagrams showing the densities of parental forms and Fi and F 2 generations of a cross between 
the Pyramidatum and Jet barleys (upper) and of four homozygous forms from this cross in the F 3 
generation (lower). 

in the F 2 generation. Hanna X Zeocriton, however, produced a much 
smaller proportion of homozygous forms in F 3 and F 4 than the 
Pyramidatum-Jet cross. Homozygous intermediates as well as forms 
with the parental densities were produced in the F 3 generation. The 
heterozygous lines were of different types, some being as variable as 
the F 2 , while others were more variable than the pure forms, but less 
so than the F 2 generation. The means of the heterozygous forms 
were also of different values. The results are illustrated in figure 2. 
These graphs show the parental and F 2 types and four pure F 3 forms 
of unlike densities, as well as the heterozygous lines obtained. This 
cross has given nearly all sorts of densities, and by this one cross the 
different densities of the parental forms used in these experiments 
have been again obtained. 



INHERITANCE IN THE BARLEY SPIKE. 



23 



These results show that, although density is a very stable size 
character, in some crosses numerous factors are involved which, by 
recombination, produce homozygous forms showing an almost con- 
tinuous range of density from the very lax to the dense types. It is 
only reasonable to conclude that if a greater number of varieties had 
been studied, together with crosses between them, a continuous range 
for the average length of internode of homozygous forms could be 
obtained which would show only small differences in average density 
between types. These results are of considerable interest in barley 
classification. While dependable in the isolation and description of 



C«7 



20 

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3V 






































r 


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s 


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fan 


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Fig. 2.— Diagrams showing the densities of parental forms and of the F 2 generation in a cross between 
the Zeocrlton and Hanna barleys (upper), of four pure lines (middle), and of several heterozygous 
lines (lower). 

strains, groups founded on this character are likely to overlap and 
] km ice to be of limited value for taxonomic purposes. 

While the general genetic results of these crosses are explained on 
a broad factor basis of differences of one to three factors, the fact 
remains that the homozygous segregates corresponding to the parents 
do not always have the exact density of the parents. Likewise, the 
forms homozygous for intermediate densities do not all fall together 
but in groups, which, in the Hanna X Zeocriton cross become almost 
continuous, even where limited numbers are concerned, and might 
become wholly continuous if it were possible to carry the full number 
to the fourth generation. Obviously, there are modifying factors, 
and so far as they affect density they may be considered as minor 
density factors. Several explanations are possible. These varia- 



24 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 

tions may be associated with the same variability which manifests 
itself in seasonal fluctuations. They may be due to the differences 
in the progressive density from the base to the tip of the rachis, which 
is more marked in some than in other varieties. Other explanations 
might be suggested, but in the absence of definite proof it seems 
unwise to attempt a more detailed analysis of the results. 

CONCLUSIONS. 

Despite the handicaps of the investigations, a number of points are 
established. 

(1) Internode length in the barley rachis is a very stable character, 
which is much less affected by environmental conditions than many 
size characters. 

(2) Segregation occurs in the F 2 generation of crosses, and forms 
homozygous for density appear in this generation, their purity being 
demonstrated in the F 3 generation. 

(3) In some crosses new lines with densities differing much from 
those of their parents can not be secured, while in others lines with 
very different densities may be isolated. 

(4) The inheritance of internode lengths may be interpreted on the 
factor hypothesis. Some of the crosses studied apj:>eared to differ 
by a single main factor of density, while in others two or three main 
factors are necessary to explain the genetic results. Minor factors 
were evident whose number or nature was not established and through 
whose action the means of homozygous forms of intermediate 
densities in some crosses may become more or less continuous between 
the means of the parents. 



LITERATURE CITED. 

(1) Alefeld, F. G. C. 

1866. Landwirtschaftliche Flora . . . 363 p. Berlin. 
Atterberg, Albert. 

(2) 1889. Die Erkennung der Haupt-Varietaten der Gerste in den nordeuro- 

paischen Saat-und Malzgersten. In Landw. Vers. Stat., Bd. 36, p. 23-27. 

(3) 1891. Die Klassification der Saatgersten Nord-Europas. In Landw. Vers. 

Stat., Bd. 39, p. 77-80. 

(4) 1899. Die Varietaten und Fnrmen der Gerste. In Jour. Landw., Bd. 47, 

Heft 1, p. 1-44. 

(5) Beaven, E. S. 

1902. Varieties of barley. In Jour. Fed. Inst. Brewing, v. 8, no. 5, p. 542- 
593, 12 fig. Discussion, p. 594-600. 

(6) Biffen, R. H. 

1907. The hybridization of barleys. In Jour. Agr. Sci., v. 2, pt. 2, p. 
183-206. 

(7) Blaringhem, L. 

1910. Etudes sur 1 'amelioration des cms d'orges de brasserie. 288 p., illus. 

(8) Eriksson, Jacob. 

1889. Collectio cerealis. Varietates cerealium in Suecia maturescentes 
continens, fasc. 1, 10 p., 2 fig. Stockholm. 
Harlan, H. V. 

(9) 1914. Some distinctions in our cultivated barleys with reference to their 

use in plant breeding. U. S. Dept. Agr. Bui. 137, 38 p., 16 fig. 
Literature cited, p. 37-38. 

(10) 1918. The identification of varieties of barley. U. S. Dept. Agr. Bui. 622, 

32 p., 4 pi. Literature cited, p. 31-32. 
Heuze, Gustave. 

(11) [1872.] Les plantes alimentaires. 2 v., illus. Paris. 

(12) 1896-97. Les plantes cereales. Ed. 2, 2 v., illus. Paris. 

KOERNICKE, F. A. 

(13) 1873. Systematische Uebersicht der Cerealien und monocarpischen Legumi- 

nosen . . . 55 p., 1 tab. Bonn. 

(14) 1882. Die Saatgerste. Hordeum vulgare 1. 'sensu latiere. In Ztschr. 

Gesam. Brauw., Jahrg. 5, p. 113-138, 161-172, 177-186, 193-203, 205- 
208, 304-311, 329-336, 393-413. PI. 5-14. 

(15) 1885. Handbuch der Getreidebaues. 2 Bd. Berlin. 

(16) 1895. Die hauptsachlichsten Formen der Saatgerste ... 15 p. Bonn. 

(17) 1908. Die Entstehung und das Verhalten neuer Getreidevarietaten. In 

Arch. Biontol., Bd. 2, Heft 2, p. 389-437. 

(18) LlNNE [LlNN^SXTS], CARL VON. 

1753. Species plantarum ... t. 1. Holmiae. 

(19) Newman, L. H. 

1912. Plant breeding in Scandinavia. 193 p., 63 fig. Ottawa. Literature 

cited, p. 188-193. 

25 



26 BULLETIN 869, U. S. DEPARTMENT OF AGRICULTURE. 

(20) Nilsson-Ehle, H. 

1909. Kreuzungsuntersuchungen an Hafer und Weizen. 122 p. Lund. 

(21) Parker, W. H. 

1914. Lax and dense eared wheats. In Jour. Agr. Sci., v. 6, no. 3, p. 371-386, 
fig. 1, pi. 1. 

(22) SCHUEBLER, GuSTAV. 

[1818.] Dissertatio inauguralis botanica sistens characteristicen et descrip- 
tiones cerealium in horto academico Tubingensi et in Wiirtem- 
bergia ... 47 p., pi. Tubingae. Inaug. Diss. 

(23) Seringe, N. C. 

1841-42. Descriptiones et figures des cereales Europeennes. In Ann. Soc. 
Roy. Agr. Lyon, t. 4, p. 321-384, pi. 1-9, 1841; t. 5, p. 103-196, pi. 
2-10, 1842. 

(24) Tschermak, Erich von. 

1914. Die Verwertung der Bastardierung fur phylogenetische Fragen in der 
Getreidegruppe. In Ztschr. Pflanzenziicht., Bd. 2, Heft 3, p. 
291-312. 

(25) Voss, A. 

1885. Versuch einer neuen Systematik der Saatgerste. In Jour. Landw., 
Jahrg. 33, Heft 3, p. 271-282. 



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